Emulsion polymerization process

Abstract

A process for reducing the residual monomer level of a polymer latex prepared by emulsion polymerization comprises exposing the latex in a separate vessel from that in which the main polymerization has been carried out to conditions under which free radicals are produced by a secondary catalyst added to the latex, the said catalyst being oil soluble or having an oil soluble component. In a preferred embodiment a polymer latex prepared by the emulsion polymerization of styrene alone or a mixture containing styrene having a residual styrene level not exceeding 0.1% based on latex volume may be obtained.

What we claim is: 
     
       1. A process for reducing the residual styrene monomer level of a polymer latex prepared by the emulsion polymerisation of styrene monomer alone, or of a monomeric mixture containing styrene monomer which polymerisation has been taken to a conversion of at least 90%, which comprises exposing the latex, in a separate vessel from that in which the main polymerisation has been carried out to conditions under which free radicals are produced by a secondary redox catalyst, said catalyst having two components, one of which is oil soluble, and at least one component of which is water soluble and is added to the latex, the only monomers in said separate vessel being those left over from said conversion and wherein the residual styrene is reduced to a level not exceeding 0.1% based on the latex volume. 
     
     
       2. A process for reducing the residual vinyl aromatic monomer level of a polymer latex prepared by the emulsion polymerisation of a vinyl aromatic monomer alone, or of a monomeric mixture containing a vinyl aromatic monomer which polymerisation has been taken to a conversion of at least 90% and there is present 0.5 to 5% of residual monomer in the latex which comprises exposing the latex in a separate vessel from that in which the main polymerisation has been carried out to conditions under which free radicals are produced by a secondary redox catalyst, said catalyst having two components, one of which is oil soluble, and at least one component of which is water soluble and is added to the latex, the only monomers in said separate vessel being those left over from said conversion and reducing the residual monomer to not over 0.1%. 
     
     
       3. A process according to claim 2 in which the oxidising component is cumene hydroperoxide, tertiary-butyl hydroperoxide, paramenthane hydroperoxide or diisopropyl benzene hydroperoxide. 
     
     
       4. A process according to claim 3 in which the activator component of the redox catalyst is diethylene triamine, triethylene tetraethylene pentamine. 
     
     
       5. A process according to claim 2 in which the oxidising component of the redox catalyst is included with the reactor charge of the main polymerisation, the activator component initiating the production of free radicals by the secondary catayst being added to the latex after the latex has been removed from the vessel in which the main polymerisation has been carried out. 
     
     
       6. A process according to claim 2 in which or the oil soluble component thereof is included with the reactor charge of the emulsion polymerisation, the conditions of the polymerisation being such that free radicals are not produced by the secondary catalyst during the polymerisation stage. 
     
     
       7. A process according to claim 6 in which there is included the oxidizing component of a redox catalyst with the reactor charge of the main polymerisation and the activator component initiating the production of free radicals by the secondary catalyst is added to the latex after the latex has been removed from the vessel in which the main polymerisation has been carried out. 
     
     
       8. A process according to claim 2 in which the polymer latex is selected from a polystyrene latex, an acrylonitrile butadiene styrene polymer latex and a carboxylated latex prepared by the polymerisation of a monomer mixture comprising butadiene, styrene and one or more unsaturated acids. 
     
     
       9. A process according to claim 2 wherein there is polymerized styrene alone and the amount of residual monomer initially present is not over 3%. 
     
     
       10. A process according to claim 9 wherein the amount of residual monomer initially present is 1.2 to 3%. 
     
     
       11. A process according to claim 2 in which the activator component of the redox catalyst is diethylene triamine, triethylene tetramine or tetraethylene pentamine. 
     
     
       12. A process according to claim 2 wherein the activator component is added to the latex.